Double talk detector

Abstract

A double talk detector for controlling the echo path estimation in a telecommunication system by indicating when a received coded speech signal is dominated by a non-echo signal; i.e., that so-called double talk exists. This is determined by extracting LSPs from a coded speech frame of the received coded speech signal when the signal power exceeds a first threshold value, converting each of said extracted LSPs into LSFs, and calculating the distance between each two adjacent LSFs. For each distance that is smaller than a second threshold, a spectral peak is located between the two LSFs, and it is determined whether said spectral peak is an echo or not. When a predetermined number of non-echo spectral peaks are located in the received speech signal, double talk will be indicated, and the echo path estimation may be disabled.

1. A method of detecting that a received coded speech signal is dominated by a non-echo signal, comprising the steps of:
 if the signal power of a received speech signal exceeds a first threshold value, then extracting the Line Spectral Pairs (LSPs) from a coded speech frame of said received speech signal; 
 converting each of said extracted LSPs into Line Spectral Frequencies (LSFs), ωi, and calculating the distance between each two adjacent LSFs; and, 
 for each of said distances that is smaller than a second threshold value, calculating the frequency of the spectral peak, ωc, surrounded by said LSFs, and determining whether said spectral peak is an echo. 
 
     
     
       2. A method according to  claim 1 , comprising the further steps of:
 incrementing a counter for each located spectral peak that is not an echo; 
 indicating double-talk when the counter reaches a predetermined threshold value. 
 
     
     
       3. A method according to  claim 1 , wherein the determination of whether a spectral peak is an echo comprises the steps of:
 extracting the LSPs from a coded speech frame of a first speech signal and converting said LSPs into the corresponding LSFs; and, 
 determining that said spectral peak is an echo if the distance between the adjacent LSFs surrounding said spectral peak in the first speech signal is smaller than a third threshold value. 
 
     
     
       4. A method according to  claim 1 , further comprising determining whether a spectral peak is an echo only if the frequency of said spectral peak is lower than a fourth threshold value. 
     
     
       5. A method according to  claim 3 , further comprising searching for a closely located second spectral peak in the first speech signal if said spectral peak is not an echo, comprising the steps of:
 calculating a second spectral peak in the first speech signal from two adjacent LSFs; and, 
 determining that said second spectral peak is an echo if the distance between the calculated second spectral peak and the centre frequency is smaller than a fifth threshold value. 
 
     
     
       6. A method according to  claim 1 , wherein the LSFs are obtained by converting each of the extracted LSPs into the corresponding LSF using the relationship qi=cos(ωi). 
     
     
       7. A method according to  claim 1 , wherein the centre frequency of a spectral peak is determined by locating two adjacent LSPs, ωi+1−ωi, and calculating ωc=(ωi+1−ωi)/2. 
     
     
       8. A method according to  claim 2 , wherein, an indication of double talk deactivates an echo path estimation in a telecommunication system. 
     
     
       9. A method of estimating an echo path in a telecommunication system, wherein the echo path estimation is deactivated by a double talk indication obtained by a method according to  claim 2 . 
     
     
       10. A method of estimating the echo path in a telecommunication system, wherein the echo path estimation is deactivated when a received coded speech signal is dominated by a non-echo-signal, the method comprising the steps of:
 if the signal power of a received speech signal exceeds a first threshold value, then extracting the Line Spectral Pairs (LSPs) from a coded speech frame of said received speech signal; 
 converting each of said extracted LSPs into a corresponding Line Spectral Frequency (LSF), ωi, and calculating the distance between each two adjacent LSFs; 
 for each distance that is smaller than a second threshold value, calculating the frequency of the spectral peak, ωc, surrounded by said LSF, and determining whether said spectral peak is an echo; and, 
 deactivating the echo path estimation when a predetermined number of spectral non-echo peaks are located. 
 
     
     
       11. A method according to  claim 10 , wherein the determination of whether a spectral peak is an echo comprises the steps of:
 extracting the LSPs from a coded speech frame of a first speech signal and converting each extracted LSP into the corresponding LSF; and, 
 determining that said spectral peak is an echo if the distance between the LSFs surrounding said spectral peak in the first speech signal is smaller than a third threshold value. 
 
     
     
       12. A method according to  claim 10 , further comprising determining whether a spectral peak is an echo only if the frequency of said spectral peak is lower than a fourth threshold value. 
     
     
       13. A method according to  claim 10 , wherein the speech coding is based on AMR-CELP-coding. 
     
     
       14. A double talk detector arranged to be connected to a coded received speech signal and to a coded transmitted first speech signal in a telecommunication system for determining when said received speech signal is dominated by a non-echo signal, the double talk detector comprising:
 a signal power monitor arranged to determine when the signal power of a received speech signal exceeds a first threshold value; 
 a spectral peak locator arranged to:
 extract the LSPs from a coded speech frame of the received speech signal and to convert each of said extracted LSPs into a corresponding LSF; and, 
 calculate the distance between each two adjacent LSFs, and calculate a spectral peak, ωc, surrounded by two LSFs separated by a distance that is smaller than a second threshold value; and, 
 
 an echo locator arranged to determine whether a located spectral peak is an echo. 
 
     
     
       15. A double talk detector according to  claim 14 , further arranged to indicate that said received speech signal is dominated by a non-echo signal if a predetermined number of spectral non-echo peaks are located in the received signal. 
     
     
       16. A double talk detector according to  claim 14 , further comprising a counter for counting the number of spectral non-echo peaks in the received speech signal. 
     
     
       17. A double talk detector according to  claim 14 , wherein the echo locator is arranged to:
 extract the LSPs from a coded speech frame of the first speech signal and convert said extracted LSPs into the corresponding LSFs; and, 
 calculate the distance between the adjacent LSFs surrounding said spectral peak and determine that the spectral peak is an echo if said calculated distance is smaller than a third threshold value. 
 
     
     
       18. A double talk detector according to  claim 14 , wherein the echo locator is arranged to determine whether a spectral peak is an echo only if the frequency of said spectral peak is lower than a fourth threshold value. 
     
     
       19. A double talk detector according to  claim 17 , wherein said echo locator is further arranged to search for a closely located second spectral peak in the first speech signal, if said spectral peak is not an echo, by:
 calculating a second spectral peak from said LSPs and determining that said second spectral peak is an echo if the distance to the centre frequency is smaller than a fifth threshold value. 
 
     
     
       20. A double talk detector according to  claim 14 , wherein the LSFs are obtained by converting each of the extracted LSPs into the corresponding LSF using the relationship qi=cos(ωi). 
     
     
       21. A double talk detector according to  claim 14 , wherein the centre frequency of a spectral peak is determined by locating two adjacent LSFs, ωi+1−ωi, and calculating ωc=(ωi+1−ωi)/2. 
     
     
       22. An echo path estimating device for a telecommunication system, arranged to deactivate the estimation of an echo path dominated by a non-echo-signal, comprising a double talk detector for a coded speech signal according to  claim 14 . 
     
     
       23. An echo path estimating device for a telecommunication system, arranged to deactivate the estimation of an echo path dominated by a non-echo-signal, the echo path estimating device comprising:
 a double talk detector arranged to be connected to a coded received speech signal and to a coded transmitted first speech signal in said telecommunication system, said double talk detector comprising:
 a signal power monitor arranged to determine when the signal power of a received speech signal exceeds a first threshold value; 
 a spectral peak locator arranged to:
 extract Line Spectral Pairs (LSPs) from a coded speech frame of the received speech signal and to convert each of said extracted LSPs into a corresponding Line Spectral Frequency (LSF), ωi; 
 calculate the distance between each two adjacent LSFs, and calculate a spectral peak, ωc, surrounded by two LSFs separated by a distance that is smaller than a second threshold value; and, 
 
 
 an echo locator arranged to determine whether a located spectral peak is an echo. 
 
     
     
       24. An echo path estimating device according to  claim 23 , wherein the double talk detector is further arranged to indicate that said received speech signal is dominated by a non-echo signal if a predetermined number of spectral non-echo peaks are located in the received signal. 
     
     
       25. An echo path estimating device according to  claim 24 , wherein the double talk detector comprises a counter for counting the number of spectral non-echo peak in the received signal. 
     
     
       26. An echo path estimating device according to  claim 23 , wherein the echo locator is further arranged to:
 extract the LSPs from a coded speech frame of the first speech signal, and convert said extracted LSPs into the corresponding LSFs; and, 
 calculate the distance between the adjacent LSFs surrounding said spectral peak and determine that the spectral peak is an echo if said calculated distance is smaller than a third threshold value. 
 
     
     
       27. An echo path estimating device according to  claim 23 , wherein the echo locator is arranged to determine whether a spectral peak is an echo only if the frequency of said spectral peak is lower than a fourth threshold value. 
     
     
       28. An echo path estimating device according to  claim 26 , wherein said echo locator is further arranged to search for a closely located second spectral peak in the first speech signal if said spectral peak is not an echo, by calculating a second spectral peak from two adjacent LSFs, and determining that said second spectral peak is an echo if the distance to the centre frequency is smaller than a fifth threshold value.